The invention relates to the field of petroleum processing or petrochemistry, concretely processes for processing hydrocarbons and apparatus for carrying them out, in particular to motor fuels as are described in Ullmann's Encyclopedia of Industrial Chemistry, Vol. A 16, Verlag Chemie Weinheim, 1990, pp. 719-753; the entire contents of this publication are hereby incorporated by reference.
Catalytic reforming is generally a refining step in petrochemistry, in particular the thermal and/or catalytic conversion of certain petroleum products, in particular heavy naphthas and so-called straight-run petrols, into aromatics and isoparaffins. The purpose of reforming is to increase the octane number of motor fuels and also to obtain byproducts suitable for the chemical industry, such as the BTX fraction. The details of reforming are well documented; reference is here made only by way of example to Ullmann's Encyclopedia of Industrial Chemistry, Vol. A 18, Verlag Chemie Weinheim, 1991, pp. 51-99, in particular pp. 67-70 (Catalytic Reforming).
E. V. Smidovich, Tekhnologya pererabotky nefty i gaza, "Khimya" publishers, Moscow, 1968, part 2, pp. 243-245 (1) discloses a process for producing petrol of high octane number by catalytic reforming of petrol fractions of low octane number at temperatures of 500.degree..+-.50.degree. C. and a pressure of up to 3.5 MPa with dilution of the feed mixture by a circulated hydrogen-containing gas in an amount of 1500 standard m.sup.3 /standard m.sup.3 of feed mixture at a molar concentration of hydrogen in the hydrogen-containing circulated gas of at least 75% in the presence of an alumino platinum catalyst having a metallic platinum content of at most 0.63% at a space velocity of the feed mixture of from 1.5 to 1.8 standard m.sup.3 /standard m.sup.3 of catalyst.
The starting mixture and the steam/gas mixture are passed through the catalyst bed parallel to the vertical axis (axially) of the reactor which is a verti cal cylindrical vessel having an axial, fully metallic tube for drawing off a gaseous product mixture and a perforated metallic insert arranged therein, with a catalyst bed being located between the walls of the insert and the central tube.
However, this process for producing petrol of high octane number has the following disadvantages:
1. high hydraulic losses when the steam/gas mixture passes through the catalyst bed, owing to a high linear flow velocity because of the limited effective cross-sectional area of the catalyst bed; PA1 2. the presence of catalyst dust which, under the process conditions, collects at the outlet of the gaseous product mixture from the catalyst bed and reduces the effective cross-section; PA1 3. increased pressure in the system which shifts the chemical conversion of the hydrocarbon starting material in the direction of the formation of low-value reforming products (byproducts); the proportion of hydrocracking products increases. PA1 1. insufficient yield of product--up to 93.86% (cf. Example 1 which reproduces the prior art); PA1 2. the low octane number of the product--77.2 MON (motor octane number).
As regards its technology, the process of the invention comes closest to a process disclosed in Khimya i tekhnologya topliv i masel, "Khimya" publishers, Moscow, 1966, No. 3, p. 14 (2) for producing petrol of high octane number by catalytic reforming of a mixture of hydrogen and hydrocarbons by passing this mixture through a platinum/rhenium catalyst arranged in the form of a hollow cylinder at 450.degree.-500.degree. C. and a pressure of 1.5-3 MPa. The feed mixture flows in the direction from the circumference of the reactor to the axis thereof. The platinum/rhenium catalysts used in this process are known and commercially available.
The petrol of high octane number is produced by catalytic reforming of petrol fractions of low octane number at a temperature of 450.degree.-500.degree. C. and a pressure of 2.8 to 5.0 MPa with dilution of the feed mixture by hydrogen-containing circulated gas in an amount of 1500 standard m.sup.3 /standard m.sup.3 of feed at a molar concentration of the hydrogen in the hydrogen-containing circulated gas of 85% (the molar ratio of hydrogen to feed is generally 8:1) in the presence of the platinum/rhenium catalyst having a metallic platinum content of 0.30-0.65% at a space velocity of the feed mixture of 1.5-1.8 m.sup.3 /h per m.sup.3 of catalyst.
The disadvantages of this process are: